1. Field of the Invention
The present invention relates to a hydrophilicity-restoring agent for removing inorganic matter from a hydrophilic surface such as a hydrophilic film whose hydrophilicity has been reduced by the adhesion of the inorganic matter to thereby restore the hydrophilicity of the hydrophilic surface, and to a method for restoring the hydrophilicity of a hydrophilic surface using the hydrophilicity-restoring agent.
2. Description of the Related Art
Japanese Patent Laid-Open Nos. 8-11631 and 10-036144 describe an anti-fog element such as a mirror for vehicles which has anti-fog properties by making its surface hydrophilic. The anti-fog element described in Japanese Patent Laid-Open No. 8-11631 is obtained by forming a hydrophilic oxide film of porous SiO2 or the like on a substrate surface. The anti-fog element described in Japanese Patent Laid-Open No. 10-036144 is obtained by forming a photocatalyst film of TiO2 or the like on a substrate surface and subsequently forming a hydrophilic oxide film of porous SiO2 or the like thereon.
The hydrophilicity of an anti-fog element is gradually reduced during its use by the adhesion of organic and inorganic matter to the hydrophilic surface. In particular, when the surface is a porous hydrophilic surface, organic and inorganic matter are liable to adhere thereto. Organic stains can be removed by utilizing photocatalyst function described in Japanese Patent Laid-Open No. 10-036144 or a surfactant described in Japanese Patent No. 3684913 or the like, but inorganic stains cannot be removed either by photocatalyst function or a surfactant. In particular, when the surface is a porous hydrophilic surface, inorganic stains enter into the pores, making it difficult to remove the stains. Further, if the inorganic stains are to be removed by strong acid, polishing, or the like, the hydrophilic surface will be damaged.
The present invention has been made in the light of the above-described problems. Accordingly, it is the object of the present invention to provide a hydrophilicity-restoring agent for removing inorganic matter from a hydrophilic surface whose hydrophilicity has been reduced by the adhesion of the inorganic matter to thereby restore the hydrophilicity of the hydrophilic surface, and to provide a method for restoring the hydrophilicity of a hydrophilic surface using the hydrophilicity-restoring agent.